A study on monkeys by anatomists at the University of Hong Kong has debunked a theory on why humans evolved their unique red-green colour vision.
The theory espoused since 1879 is that the three-pigment (primary colours red, blue and yellow) eye structure allowed humans to look for ripe fruits against green foliage.
But according to research by American graduate student Nathaniel Dominy and Professor Peter Lucas of the department of anatomy at the university, this vision is suited for foraging for young leaves, not fruit.
Their study, published in Nature magazine, was based on observing the eating habits of four species of monkeys and chimpanzees in Uganda, which share the same eye structure as humans.
Humans are unique among mammals in that our eyes have three pigments, which are tuned to red-green channels. This tri-chromatic colour vision is also found among 'old world' monkeys such as Hong Kong's macaques, apes and chimpanzees.
Professor Lucas suggested in 1998 that the eye structure was suited for leaf food selection. He noticed young leaves were usually red in the tropics. 'The results implicate leaf consumption, a critical food resource when fruit is scarce, as having unique value in maintaining tri-chromacy,' the article said.
Mr Dominy, a 24-year-old student from Pennsylvania, said the findings could explain why there had been increasing colour-blindness among Caucasian men.
'Maybe we are losing our colour vision because we have not been in the forest for a very long time to look for food,' he said.